1. Field of the Invention
The present invention relates to an electron beam direct writing technique by which circuit patterns of a semiconductor device are written by repeatedly exposing minute shaped beams, and in particular, to an electron beam writing method, an electron beam writing apparatus which draw patterns by using a variable shaped beam (VSB) and a character projection (CP), and a semiconductor device manufacturing method.
2. Description of the Related Art
In electron beam lithography, in particular, electron beam direct writing technique, when a circuit pattern is transcribed onto a resist on a semiconductor substrate, there in no need to prepare a corresponding mask of a circuit pattern for each of the devices having different circuit patterns. Further, the wavelength of an electron beam is much shorter than the wavelength of a light-source light used for light exposure writing, and it is therefore possible to form a fine pattern. Therefore, the electron beam direct writing technique is applied to the research and development of a prototype QTAT (Quick Turn Around Time) device, a fine edge device or the like.
In electron beam lithography, a circuit pattern is broken up into a plurality of basic graphic figures, which are units of exposure. Then, electron beams having shapes and sizes which are the same as those of the respective basic graphic figures are shaped by using a plurality of shaping apertures. The shaped electron beams are sequentially irradiated onto a resist. Each irradiation of an electron beam is called a shot. As methods for shaping electron beams, there are two types: a variable shaped beam (VSB) method and a character projection (CP) method. In the variable shaped beam (VSB) method, patterns broken up into a rectangle, a triangle, and a trapezoid, which are the basic graphic figures, are inputted and the overlapping of two shaping apertures is controlled to form rectangular and triangular electron beams. On the other hand, in the character projection (CP) method, openings having shapes which are the same as the basic shapes are formed in shaping apertures, the shape of the cross section of the electron beam is made into a basic shape (which is called a character), and an electron beam is deflected to pass through the corresponding opening of a shaping aperture when a pattern which is the same as a shape of an opening is inputted. In an electron beam writing apparatus using the CP method, generally, not only the CP method in which a shape of cross section of an electron beam is shaped into a basic shape (character) formed in a shaping aperture, but also the VSB method in which rectangular and triangular electron beams are shaped by controlling the overlapping of two shaping apertures are used. A shaping aperture having a character shaped opening is called a CP aperture, and the number of character openings selectable by deflecting electron beams is generally several to several hundred (Jpn. Pat. Appln. KOKAI Publication No. 10-284385, Jpn. Pat. Registration No. 2512184, and Jpn. Pat. Registration No. 2526326).
A conventional electron beam writing apparatus has an electron beam writing device having an electron gun, various deflection systems, various lens systems, and a stage system, or the like, and a writing control circuit 70 as shown in FIG. 7 which outputs a signal for controlling the deflection systems and the stage system of the electron beam writing apparatus corresponding to electron beam writing data.
The writing control circuit 70 has a pattern data expanding circuit 71, an irradiation amount correction circuit 72, a shot dividing circuit 73, an irradiation time determining circuit 74, and a shot position correction circuit 75.
Each pattern data in electron beam writing data expressed by basic graphic figures is expanded by the pattern data expanding circuit 71. The expanded pattern data is corrected with regard to the irradiation amount of electron beam by the irradiation amount correction circuit 72. The irradiation amount correction is typically proximity correction. The corrected pattern data is divided by the shot dividing circuit 73 into patterns having shapes and sizes of formable electron beams. For each pattern, an irradiation time of an electron beam irradiated onto the substrate is determined by the irradiation time determining circuit 74. On the other hand, for each pattern, the electron beam onto the substrate is corrected with regard to the shot position by the shot position correction circuit 75. Then, signals are outputted to a blanking control unit, an electron beam deflection unit, and a stage control unit.
Correction of the irradiation position is performed to correct misalignment of patterns, distortion due to the deflection of an electron beam, or the like. This correction is carried out by feeding an output control signal of the stage control unit for controlling a position of the stage back to the deflection system to correct a signal to be inputted to the writing control circuit 70.
However, there has been the following problem in this type of electron beam writing apparatus. Namely, the number of shots necessary for carrying out writing cannot be determined until electron beam writing data is inputted to the writing control circuit and the pattern data is expanded. Further, an irradiation amount of an electron beam in each shot cannot be determined until writing processing is started. Therefore, the time taken for writing processing cannot be known in advance of the writing processing. In order to know the time taken for writing processing, it is necessary to confirm the writing processing time by actually writing, or to determine the writing processing time by a simulation using electron beam writing data.
Determining the writing processing time by such methods means that writing processing which is not originally required is carried out, and processing carried out mainly by hardware (control circuit) at the time of writing is carried out by software in advance, which take extra time. These processing increase the raw process time (RPT) in electron beam writing in the lithography stage in the semiconductor manufacturing process.
Further, it is impossible to confirm whether or not each shot data generated in the writing control circuit is correct. Therefore, it is difficult to carry out detailed handling of correction of an irradiation amount with respect to a shot pattern.
In this way, conventionally, in an electron beam writing apparatus, in order to determine a writing processing time in advance of the writing processing, processings in which originally unnecessary writing processing is carried out, processing which is carried out mainly by hardware (control circuit) at the time of writing is carried out by software in advance are required. These processing have led to the problem that RPT by electron beam writing in the semiconductor manufacturing process is made longer. Further, there has been the problem that it is impossible to carry out detailed handling of correction of an irradiation amount or the like with respect to a shot pattern.